Component line 04 / Hydrogen & gas detection
Hydrogen detection for battery rooms, UPS rooms and data centres
Catalytic combustion detectors reading 0 to 100 % LEL, electrochemical detectors reading 0 to 1000 ppm, alarm controllers with selectable 10, 30 and 40 % LEL setpoints, and the relay that starts the exhaust fan and proves it started. Supplied as components. The ventilation design and the interlock logic belong to your designer of record.
Standard references only. Hazardous area certification depends on the model and the enclosure; the certificate with its document number states the area classification claimed.
Hydrogen ignites between 4 % and 75 % by volume in air. The lower figure is the one that matters and everything on this page is measured against it.
Two sensors, because they answer two different questions
A catalytic detector tells you how close the room is to a flammable mixture. An electrochemical detector tells you a cell is venting long before that. A battery room needs both answers, and they are not interchangeable.
The catalytic bead burns a tiny sample on a heated element and measures the heat the reaction produces, which is why it reads in percent LEL and why it needs oxygen present to work at all. The electrochemical cell oxidises hydrogen at an electrode and produces a current proportional to concentration, which is why it reads in parts per million and why it keeps working in a sealed, oxygen-displaced enclosure where a catalytic sensor would struggle.
Engineering note · what the setpoints mean in ppm
Ten per cent LEL is 0.4 % by volume, which is 4 000 ppm. Thirty per cent is 1.2 % by volume, 12 000 ppm. Forty per cent is 1.6 % by volume, 16 000 ppm. Those numbers matter because an electrochemical detector scaled 0 to 1000 ppm will be off its scale long before a 10 % LEL alarm is reached, which is exactly why the two devices are installed as a pair rather than one replacing the other.
| Reading | By volume | In ppm |
|---|---|---|
| 10 % LEL | 0.4 % v/v | 4 000 ppm |
| 30 % LEL | 1.2 % v/v | 12 000 ppm |
| 40 % LEL | 1.6 % v/v | 16 000 ppm |
| 100 % LEL | 4 % v/v | 40 000 ppm |
01 / Specification
Datasheets
| Measuring range | 0 to 100 % LEL |
|---|---|
| Resolution | 1 % LEL |
| Response | T90 typically under 30 s |
| Sensor | Catalytic bead, replaceable |
| Requires oxygen | Yes, and it reads low in an inerted atmosphere |
| Known limitation | Degraded by silicone and halogenated vapours |
| Outputs | 4 to 20 mA, RS-485 Modbus, relay contacts |
| Supply | 24 V d.c. |
| Enclosure | IP65 or IP66, area classification per model |
| Ambient | −4 to 122 °F ≡ −20 to 50 °C |
| Measuring range | 0 to 1000 ppm (0 to 2000 ppm option) |
|---|---|
| Resolution | 1 ppm |
| Response | T90 typically under 60 s |
| Sensor | Electrochemical cell, replaceable |
| Cell life | Typically two years, depends on exposure |
| Cross sensitivity | Carbon monoxide and hydrogen sulphide can read as hydrogen |
| Outputs | 4 to 20 mA, RS-485 Modbus, relay contacts |
| Supply | 24 V d.c. |
| Channels | 4, 8 or 16 input channels |
|---|---|
| Inputs | 4 to 20 mA, plus digital inputs for fan proof |
| Alarm setpoints | 10, 30 and 40 % LEL, selectable and adjustable |
| Outputs | Relay per setpoint, plus a dedicated interlock relay |
| Comms | Modbus RTU or TCP to the building system |
| Event log | Time stamped, retained through power loss |
| Supply | 24 V d.c., or 110 / 230 V a.c. with a 24 V d.c. supply |
| Standby | Sealed battery, per the panel listing |
| Enclosure | IP54 wall mount panel |
| Interlock relay | Volt free contact to the fan contactor |
|---|---|
| Run-on timer | Adjustable, typically 5 to 15 minutes |
| Fan proof | Current switch or airflow switch, wired back as a digital input |
| Why proof matters | A relay that has closed proves nothing about the fan |
| Manual override | Local fan start, with the interlock left in place |
Two sensors that fail differently
A catalytic sensor that has been poisoned by a silicone sealant reads low and looks healthy while doing it. An electrochemical cell at the end of its life drifts and then stops. Both failures are quiet, which is why the commissioning routine includes a bump test with a known gas and why the cell has a replacement date rather than a lifetime.
02 / Model list
Model designations
Add what you need and the list is carried into the enquiry form. State the area classification and the installation height with the order, because both affect the housing.
| Model designation | Item | Range or function | Output | Add to model list |
|---|---|---|---|---|
| EMS-GD-H2-CAT | Hydrogen detector, catalytic | 0 to 100 % LEL | 4 to 20 mA, Modbus, relay | |
| EMS-GD-H2-ECM | Hydrogen detector, electrochemical | 0 to 1000 ppm | 4 to 20 mA, Modbus, relay | |
| EMS-GD-ECM-2000 | Hydrogen detector, electrochemical | 0 to 2000 ppm | 4 to 20 mA, Modbus, relay | |
| EMS-GD-CTRL-04 | Alarm controller | 4 channels, 10 / 30 / 40 % LEL setpoints | Relays, Modbus | |
| EMS-GD-CTRL-08 | Alarm controller | 8 channels, 10 / 30 / 40 % LEL setpoints | Relays, Modbus | |
| EMS-GD-CTRL-16 | Alarm controller | 16 channels, 10 / 30 / 40 % LEL setpoints | Relays, Modbus | |
| EMS-GD-ILK-01 | Fan interlock relay module | Volt free, with run-on timer | Relay to contactor | |
| EMS-GD-FP-01 | Fan proof switch | Current or airflow sensing | Digital input to the controller | |
| EMS-GD-CAL-KIT | Calibration and bump test kit | Regulator, tubing and cap | Not applicable | |
| EMS-GD-CELL-H2 | Replacement sensor cell | Electrochemical, hydrogen | Not applicable |
03 / Scope
What this line ships, and what it does not
Ships from us detection components
- Catalytic and electrochemical hydrogen detectors in the ranges listed
- Alarm controllers with the three setpoints and an event log
- Interlock relay modules with a run-on timer
- Fan proof switches and replacement sensor cells
- Calibration and bump test kits, with the calibration certificate and its document number
Not from us by others
- The ventilation design, the air change rate and the duct sizing
- The interlock logic and the sequence the project requires
- Detector location and height selection for the room
- Installation, cabling, conduit and termination
- Commissioning, bump testing on site and the acceptance test
- Integration with the fire alarm or building management system
04 / On site
Where the detectors go, and why
- High and at the extract. Hydrogen is the lightest element and rises, so the catalytic detector goes at the high point of the room or inside the exhaust duct where the gas collects before it leaves. A detector at standing height measures the last place the gas will be.
- At the rack for the ppm cell. The electrochemical detector goes close to the battery terminals or the rack, where a single venting cell produces a local cloud that mixes into the room before it reaches the ceiling.
- Area classification. Hydrogen sits in the most demanding gas group on both scales, Group B in the North American classification and group IIC in the IEC and ATEX system. Whether a detector needs an explosion proof housing depends on the zone the room is classified as, which the project decides.
- Ventilation references. Battery room ventilation and the interlock that proves it is running are governed by references such as IEEE 1635 for stationary battery ventilation, NFPA 855 for stationary energy storage, and the exhaust ventilation provisions for battery rooms in the international fire code family. Those design decisions sit with your engineer, not with us.
- Maintenance is a schedule, not an event. A catalytic bead and an electrochemical cell both degrade quietly. Bump testing with a known gas and replacing the cell on a date rather than on a fault is what keeps the installation honest.
Engineering note · one alarm is not enough
A single setpoint forces a choice between nuisance alarms and late alarms. Three setpoints let the project assign meaning: early warning and ventilation start at the lowest, alarm at the middle, and escalation at the top. Which figure carries which action is a design decision, and the controller is supplied with all three adjustable.
05 / Questions
Hydrogen detection, asked and answered
What does 10 % LEL of hydrogen mean in ppm?
The lower explosive limit of hydrogen in air is 4 % by volume. Ten per cent LEL is therefore 0.4 % by volume, which is 4 000 ppm. Thirty per cent LEL is 1.2 % by volume and 40 % LEL is 1.6 % by volume.
Why use both a catalytic and an electrochemical detector?
They answer different questions. The catalytic detector reads in percent LEL and drives the ventilation interlock. The electrochemical detector reads in parts per million and catches small leaks long before they approach a flammable concentration. Catalytic sensors also need oxygen present and are degraded by silicone and halogenated vapours, so the ppm cell covers the early warning role that the catalytic sensor cannot.
Do you design the battery room ventilation?
No. We supply the detectors, the controller and the interlock relay. The ventilation design and the interlock logic are the designer of record's work, and the installation and commissioning belong to the installing contractor. What we do supply is the fan proof device, so that the interlock proves the fan is running rather than assuming it.
Does the detector need an explosion proof housing?
That depends on the area classification of the room, which the project decides. Hydrogen is Group B in the North American classification and group IIC in the IEC and ATEX system, so where a hazardous area is declared the housing has to match it. Tell us the zone and we will quote the model certified for it, with the certificate and its document number.
How often does a sensor need replacing?
An electrochemical cell is typically a two year item and a catalytic bead lasts considerably longer unless it is poisoned. Both are replaceable parts and both are carried in stock. The right interval comes from the manufacturer's data and the exposure in your room, and it belongs in the maintenance schedule rather than in a fault report.
Hydrogen & gas detection
Send the room list and the zone classification
Tell us how many rooms, the area classification and whether the interlock drives a wall fan or a ducted system. The quotation comes back with the detector count, the controller size and the fan proof device.
- Catalytic
- 0 to 100 % LEL
- Electrochemical
- 0 to 1000 ppm, 2000 ppm option
- Setpoints
- 10 / 30 / 40 % LEL, adjustable
- Interlock
- Relay plus fan proof input